1. Field of Invention
This invention pertains to a temperature sensor that detects high temperature conditions caused by electrical overloads. More particularly, this invention pertains to a temperature sensor that cooperates with a circuit that interrupts the power circuit to the electrical appliance based on the temperature proximate the temperature sensor.
2. Description of the Related Art
Every year there are thousands of electrical fires in homes. Hundreds die every year in these fires, with many more injured. Some of these fires are caused by electrical system failures and defective appliances. But, many more of these fires are caused by the misuse and poor maintenance of electrical appliances, incorrectly installed wiring, and overloaded circuits and extension cords.
Electrical circuits are protected from overcurrent conditions by circuit breakers. These circuit breakers are centrally located. Fixed wiring runs from the circuit breakers to power receptacles located throughout the home. The typical receptacle is configured to receive two plugs from electrical devices. It is not uncommon for people to use adapters in order to plug more than two electrical devices into such a receptacle. Such misuse, although not commonly resulting in an overcurrent condition that will trip a circuit breaker, often exceeds the capabilities of the adapter, which may result in overheating of the adapter and/or the receptacle. Also, the adapter or one of the multitude of electrical plugs may have a high resistance connection, which results in resistance heating of the connection. Another type of misuse is the continued use of frayed or damage electrical cords. Without the protection of the circuit breaker tripping the circuit, such misuse can result in an electrical fire.
Ground fault circuit interrupters (GFCIs) are becoming more common. Ground fault circuit interrupters monitor the circuit for ground faults, and trip the circuit when one is detected. A ground fault is a condition where the current flowing through the hot lead to the device is not equal to the current flowing through the neutral lead to the device. When the two current values are not equal, then some amount of current must be flowing through a ground connection, which indicates a potential electrical safety hazard. Although GFCIs provide electrical safety to people, GFCIs do not protect against hazards that typically result in electrical fires.
Arc fault circuit interrupters (AFCIs) are also becoming common. Arc fault circuit interrupters monitor the circuit for electrical arcs, such as caused by loose connections or frayed wiring that causes a short circuit. The AFCI typically reacts to an arcing condition before a traditional circuit breaker, which operates based on current flow or thermal heating of a trip element. Arc fault circuit interrupters are an important line of defense against electrical fires, but AFCIs do not detect all conditions that result in electrical fires.
Attempts have been made to provide a device useful for reducing the number of electrical fires. For example, U.S. Pat. No. 7,400,225 discloses a receptacle that includes a fusible link that interrupts the circuit upon detecting an overheating condition, such as a glowing contact or series arcing. The fusible link opens the circuit permanently, thereby requiring replacement of the receptacle in order to return the connected devices back to service.